Magnesium-based methods, systems, and devices

ABSTRACT

An aspect of the present invention is an electrical device, where the device includes a current collector and a porous active layer electrically connected to the current collector to form an electrode. The porous active layer includes MgBx particles, where x≥1, mixed with a conductive additive and a binder additive to form empty interstitial spaces between the MgBx particles, the conductive additive, and the binder additive. The MgBx particles include a plurality of boron sheets of boron atoms covalently bound together, with a plurality of magnesium atoms reversibly intercalated between the boron sheets and ionically bound to the boron atoms.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Non-Provisional patentapplication Ser. No. 14/685,428, filed Apr. 13, 2015, which claimspriority to U.S. Provisional Application No. 61/978,317, filed Apr. 11,2014, the contents of which are incorporated by reference in theirentirety.

CONTRACTUAL ORIGIN

The United States Government has rights in this invention under ContractNo. DE-AC36-08G028308 between the United States Department of Energy andthe Alliance for Sustainable Energy, LLC, the Manager and Operator ofthe National Renewable Energy Laboratory.

BACKGROUND

Rechargeable lithium ion batteries have found considerable use inapplications such as hearing aids, computing devices, phones, andcameras. For example, lithium has served as the anode material formetal-air batteries due to its high energy density. However, the energydensities and efficiencies of currently available rechargeable lithiumion battery designs remain below what is needed for these types ofbatteries to meet the needs of the light duty transportation sector.Thus, the advancement of electrical vehicles and large-scale energystorage devices requires further development of high-energy-density,cost-effective, long lasting, and abuse-tolerant batteries. In addition,alternatives to lithium batteries are desirable due to lithium'stendency in some conditions to react violently, and due to lithium'stendency to form dendrites, which can limit lithium battery performanceand lifespan.

Magnesium-ion batteries provide an attractive alternative electrodematerial to lithium-ion batteries because magnesium is abundant and hasa low toxicity. Magnesium-ion batteries also offer the benefit oftwo-electron reactions instead of the one-electron reactions provided bylithium-ion batteries. Thus, magnesium-ion batteries may provide theenergy requirements needed to meet the needs of portable devices,electric vehicles, and energy storage applications. However, to date,magnesium-ion batteries have seen only limited success. This is at leastpartially due to the formation of electronic and ionic insulating filmson the magnesium-metal anode surfaces, in magnesium-ion batteriesutilizing either non-aqueous or aqueous electrolytes. These films reducethe ability of the magnesium metal to continuously obtain magnesiumions. The chemistry of magnesium metal in aprotic electrolytic solutionsoften results in the growth of these films, which limits the reversibledeposition/dissolution reaction of Mg/Mg²⁺. Thus, there remains a needfor safer and more functional rechargeable electrodes and batteries thatprovide better performance than the incumbent technologies, whilemaintaining economic viability.

SUMMARY OF THE INVENTION

An aspect of the present invention is an electrical device, where thedevice includes a current collector and a porous active layerelectrically connected to the current collector to form an electrode.The porous active layer includes MgB_(x) particles, where x≥1, mixedwith a conductive additive and a binder additive to form emptyinterstitial spaces between the MgB_(x) particles, the conductiveadditive, and the binder additive. The MgB_(x) particles include aplurality of boron sheets of boron atoms covalently bound together, witha plurality of magnesium atoms reversibly intercalated between the boronsheets and ionically bound to the boron atoms.

In some embodiments of the present invention, the electrical device mayinclude a second electrode and a non-aqueous liquid electrolyte, whereat least the active layer of the first electrode and the secondelectrode are immersed in the electrolyte. The first electrode may havea first state, where up to 75% of the magnesium atoms are reversiblyintercalated between the boron sheets, and a second state, where aportion of the magnesium atoms are reversibly deintercalated from theactive layer, resulting in the transfer of Mg²⁺ ions into theelectrolyte.

In some embodiments of the present invention, the electrical device mayinclude a conductive additive that is acetylene black. In someembodiments of the present invention, the electrical device may includea binder additive that is polyvinylidene fluoride. In some embodimentsof the present invention, the active layer may include a MgB₂ contentranging from about 50 wt % MgB₂ to about 80 wt % MgB₂, a conductiveadditive content ranging from about 10 wt % of the conductive additiveto about 30 wt % of the conductive additive, and where the remainder ofactive layer may be the binder additive.

In some embodiments of the present invention, a current collector may beconstructed from copper, gold, aluminum, and/or silver. In someembodiments of the present invention, the electrolyte may be a solutionof magnesium tetrahydroborate in dimethoxyethane. In some embodiments ofthe present invention, the second electrode may include magnesium metal,vanadium oxide, and/or lithium metal.

A further aspect of the present invention is a method for storing energyin a battery, where the method includes immersing a first electrode anda second electrode in a liquid, non-aqueous, Mg²⁺ ion-containing,electrolyte solution, where the first electrode includes boron sheets ofboron atoms covalently bound together, with a plurality of magnesiumatoms reversibly intercalated between the boron sheets and ionicallybound to the boron atoms. The method also includes applying a voltageacross the first electrode and the second electrode, where the voltagecauses the reversible deintercalation of a portion of the magnesiumatoms from between the boron sheets, creates a flux of Mg²⁺ ions fromthe first electrode into the electrolyte solution, and produces thereversible transfer of at least some of the Mg²⁺ ions from at least oneof the flux and/or from the electrolyte solution to the secondelectrode, such that the energy stored in the battery ranges from about6 mAh/g to about 10 mAh/g.

In some embodiments of the present invention, a method for storingenergy in a battery may include applying a load across the firstelectrode and the second electrode, such that the load produces thereversible removal of magnesium atoms from the second electrode, createsa flux of Mg²⁺ ions from the second electrode into the electrolytesolution, and produces the reversible intercalation between the boronsheets of the first electrode of at least some of the Mg²⁺ ions from atleast one of the flux from the second electrode and/or the electrolytesolution. In some embodiments of the present invention, the secondelectrode may include magnesium metal and the reversible transfer of atleast some of the Mg²⁺ ions to the second electrode may be byelectrochemical plating of Mg²⁺ ions onto the magnesium metal. In someembodiments of the present invention, the second electrode may includevanadium oxide and the reversible transfer of at least some of the Mg²⁺ions to the second electrode may be by intercalation of Mg²⁺ ions intothe vanadium oxide.

A further aspect of the present invention is a rechargeablemagnesium-based air battery that includes an anode layer formed ofmagnesium boride having the formula MgB_(x), where x≥1, and is depositedonto a first support structure, a porous cathode layer, where the layerincludes positive active material that at least activates carbon forabsorbing oxygen in air, and where oxygen gas is used as the positiveactive material and is deposited onto a second support structure. Therechargeable magnesium-based air battery also includes an electrolyte,where the electrolyte is a non-aqueous solution where the solutioncontains Grignard reagents such as RMgX. The anode layer and cathodelayer are connected electrically and the electrolyte is in contact withthe first and second support structures.

In some embodiments of the present invention, the first and secondsupport structures of a rechargeable magnesium-based air battery may bepositive and negative current collectors. In some embodiments of thepresent invention, the anode layer may be doped. In some embodiments ofthe present invention, the anode layer may be doped with at least one ofa Group IV/Group 14 element and/or a Group V/Group 15 element. In someembodiments of the present invention, the Group IV/Group 14 element mayinclude at least one of carbon, silicon, germanium, tin, lead,flerovium, and/or combinations thereof. In some embodiments of thepresent invention, the Group V/Group 15 element may include at least oneof nitrogen, phosphorous, arsenic, antimony, bismuth, and/orcombinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an active material for an electrode, includingreversibly intercalated/deintercalated magnesium atoms/ions betweenboron sheets, according to exemplary embodiments of the presentinvention.

FIG. 2 illustrates an active material for an electrode, includingreversibly intercalated/deintercalated magnesium atoms/ions betweensheets of vanadium oxide, according to exemplary embodiments of thepresent invention.

FIG. 3 illustrates an electrical device, according to exemplaryembodiments of the present invention.

FIG. 4 illustrates a coin battery, according to exemplary embodiments ofthe present invention.

FIGS. 5a and 5b illustrate experimental results of the reversiblecapacity for a battery including a MgB₂ first electrode, a magnesiummetal second electrode, and a Mg-ion electrolyte, according to exemplaryembodiments of the present invention.

FIG. 6 illustrates a rechargeable, magnesium-boride-based air battery,according to exemplary embodiments of the present invention.

FIG. 7 illustrates a method 200 to manufacture a rechargeablemagnesium-boride-based air battery, according to exemplary embodimentsof the present invention.

REFERENCE NUMERALS

100 . . . first electrode active material (first state)

110 . . . first electrode active material (second state)

120 . . . boron atom

130 . . . intercalated magnesium atom

140 . . . deintercalated magnesium ion

150 . . . vacancy

200 . . . second electrode active material (first state)

210 . . . second electrode active material (second state)

220 . . . vanadium atom

230 . . . oxygen atom

240 . . . intercalated magnesium atom

250 . . . vacancy

300 . . . electrical device

305 . . . first electrode

310 . . . electrode active material

320 . . . binder additive

330 . . . conductive additive

340 . . . interstitial space

350 . . . electrolyte

360 . . . current collector

400 . . . coin battery

410 . . . first case

420 . . . second case

430 . . . spring

440 . . . first electrode

450 . . . separator

460 . . . second electrode

600 . . . magnesium-boride-based air battery

602 . . . anode current collector

604 . . . anode

610 . . . cathode

620 . . . breathable layer

630 . . . diffusion layer

640 . . . carbon conductive material

650 . . . catalyst layer

660 . . . cathode current collector

670 . . . electrolyte

700 . . . method of manufacture

702 . . . fabricating a first support structure

704 . . . depositing a magnesium boride based anode

706 . . . forming a non-aqueous electrolyte

708 . . . fabricating a porous cathode layer

710 . . . depositing the electrolyte layer

DETAILED DESCRIPTION OF EXEMPLARY EMODIMENTS

FIG. 1 illustrates two reversible states 100 and 110 for an electrodeactive material constructed of MgB_(x). A plurality of covalently boundboron atoms 120 forms layers of parallel crystalline sheets with spacesin between the sheets. A plurality of magnesium atoms 130 is positionedwithin the spaces and between the sheets of boron atoms. Magnesium atomsin this position are referred to as intercalated within the crystallinestructure of the MgB_(x). X may be greater than or equal to one. In thecase of magnesium diboride, MgB₂, x is equal to two.

Applying a voltage, or alternatively, a load to a battery system thatincludes MgB_(x) as the active material for one of its two electrodes,may cause a portion of the intercalated magnesium atoms 130 to beremoved from the MgB_(x) crystalline structure as Mg²⁺ ions 140, ordeintercalate from the crystalline structure. The formation of the Mg²⁻ions 140 results in the release of 2 electrons (e⁻), which aretransferred to the second electrode through the external circuit. TheMg²⁺ ions 140 may then enter the battery's electrolyte (not shown) totravel towards the second electrode (not shown) of the battery, tocharge the battery.

This process is reversible because applying the opposite of what wasjust described, either a load or a voltage, can switch the battery fromthe second state 110 back to the first state 100. For example, ifdeintercalation of Mg²⁺ ions 140 was achieved by applying a voltage tothe battery, the original state 100 may be renewed by applying a load tothe battery. Alternatively, if deintercalation of Mg²⁺ ions 140 wasachieved by applying a load to the battery, the original state 100 maybe renewed by applying a voltage to the battery.

The reversible intercalation/deintercalation process summarized in FIG.1 for a first electrode made from a MgB_(x) containing active materialmay be represented by the following reaction, where the left side of thereaction corresponds to the first state, and the right side of thereaction corresponds to the second state:MgB_(x)

Mg_((1-y))B_(x)+(y)Mg²⁺+(2y)e ⁻  Reaction 1

FIG. 2 illustrates two exemplary reversible states 200 and 210 for asecond electrode of a rechargeable battery that includes a first MgB_(x)electrode. In this example, reversible intercalation of Mg²⁺ ions 140may also be achieved at a second electrode constructed of vanadium oxide(e.g. V₂O₅). In the first state 200, the active material includes aplurality of covalently bound vanadium atoms 220 and oxygen atoms 230,which form layers of parallel crystalline V₂O₅ sheets with spaces inbetween the sheets. These spaces provide vacancies 250 for magnesiumions 140 to move into or intercalate.

Applying a voltage, or alternatively, a load to a battery system thatincludes V₂O₅ as the active material for the second electrode, may causea portion of the Mg²⁺ ions 140 to move from the electrolyte solution(not shown) and intercalate between the sheets of V₂O₅ to occupy thevacancies 250. The electrons removed from the magnesium atoms at thefirst electrode may then counter-balance the intercalated Mg²⁺ ions toform intercalated magnesium atoms 240.

As with the MgB_(x) active material of the first electrode, a secondelectrode including V₂O₅ active material may also be reversible betweenthe two states 200 and 210. Again, as with the first electrode, applyingthe opposite of what was just described, either a load or a voltage, mayswitch the battery from the second state 210 back to the first state200. For example, if intercalation of Mg²⁺ ions was achieved by applyinga voltage to the battery, the original state 200 may be renewed byapplying a load to the battery. Alternatively, if intercalation of Mg²⁺ions was achieved by applying a load to the battery, the original state200 may be renewed by applying a voltage to the battery.

The reversible intercalation/deintercalation process summarized in FIG.2 for a second electrode made from a V₂O₅ containing active material maybe represented by the following reaction:V₂O₅+(y)Mg²⁺+(2y)e ⁻

Mg_(y)V₂O₅  Reaction 2

In some examples of a MgB_(x) containing battery, the second electrodemay be constructed using a metal active material such as magnesium metalor lithium metal. In these cases, Mg²⁺ ions may not reversiblyintercalate into the second electrode's active material. Instead, thereaction occurring in these examples may include the reversibleelectrochemical plating of magnesium metal onto the second electrode'sactive material.

FIG. 3 illustrates an exemplary electrical device 300 that utilizes theelements and features described above. In this example, a firstelectrode 305 may be constructed from a mixture of MgB₂ active material310, a conductive additive 330, and a binder additive 320 to form asolid mixture with interstitial spaces between the MgB₂ active material310, the conductive additive 330, and the binder additive 320. Themixture of the MgB₂ active material 310, the conductive additive 330,and the binder additive 320 may be applied to a surface of a currentcollector 360 to form the first electrode 305. The first electrode 305may then be immersed in an electrolyte 350. In some examples, theelectrolyte 350 may be a non-aqueous liquid, which may flow into andfill the interstitial spaces 340.

An electrode similar to the example illustrated in FIG. 3 may beprepared from slurries ranging from about 50 wt % active material toabout 99 wt % active material. For example a mixture of MgB₂ powder maybe combined with a binder additive (e.g. polyvinylidene fluoride) and aconductive additive (e.g. carbon black) in a solvent (e.g. n-methylpyrrolidone) to make a mixture. To insure a uniform distribution of thecomponents is attained, the mixture may be agitated using an appropriatemixing device. Once a uniform distribution is attained, the mixture maybe applied to the current collector (e.g. an Al and/or Cu foil) at athickness ranging from about 10 μm to about 50 μm. After the mixture hasbeen applied to the current collector, it may be dried and/or cured byheating the mixture and the current collector to a temperature rangingfrom about 50° C. to about 100° C., and maintaining the temperature fora period of time ranging from about 1 hour to about 10 hours, thusproducing the electrode. A final circular shape may be attained bypunching the foil containing the electrode mixture, using an appropriatepunching mechanism. In some examples, the MgB₂ containing electrode maybe punched into disks with diameters ranging from about 5/16 of an inchto about ½ an inch.

An electrode formed by such a method than may be utilized to fabricate acoin cell battery as illustrated in FIG. 4. For example, a coin cellbattery 400 may be constructed by separating a first electrode 440 froma second electrode 460, utilizing a separator 450. The resultant“sandwich” of the first electrode 440, the second electrode 460, and theseparator 450 may then be placed on a second case 420, followed by theaddition of electrolyte (not shown). The “sandwich” may then be securedbetween a first case 410 and the second case 420, with sufficient forcesupplied by a spring 430, to insure proper contact between all of thebattery elements. In this exemplary case, the volume of electrolyte usedmay vary from about 0.1 ml of electrolyte to about 1 ml of electrolyte.

FIGS. 5a and 5b summarize experimental data obtained from an exemplaryMgB₂ containing battery. In this example, the battery includes a cathodecontaining MgB₂ as the active material. The MgB₂ is mixed with acetyleneblack (e.g. conductive additive) and polyvinylidene fluoride (e.g.binder additive) at about 60 wt %, about 20 wt %, and about 20 wt %,respectively. This mixture is applied to a copper current collector andtreated as described above to form the cathode. In this example,magnesium metal is used as the anode. Both electrodes are placed in anelectrolyte solution of magnesium tetrahydroborate dissolved indimethoxyethane. FIGS. 5a and 5b summarize the cyclical behavior of thisexemplary battery for a total of 50 charge-discharge cycles.

Magnesium-boride-based layered materials may replace magnesium metal inMg-ion/air batteries. Magnesium boride as the anode material may alsoenable the use of non-aqueous electrolytes to achieve greater energydensities than current Li-ion technology. This disclosure describes,among other things, a magnesium boride electrode material formagnesium-based battery devices that are rechargeable, such asmagnesium-boride-air batteries.

Magnesium-boride-air batteries usually comprise three parts: amagnesium-containing anode, an air cathode and an electrolyte. Thereactions involved in an exemplary embodiment are as follows:

Anode:MgB_(x)

Mg_((1-y))B_(x)+(y)Mg²⁺+(2y)e ⁻  Reaction 3

Cathode:O₂+4e⁻

2O²⁻ or  Reaction 4O₂+2e⁻

2O⁻ or  Reaction 5O₂+e⁻

(O₂)⁻  Reaction 6

FIG. 6 illustrates an example of a magnesium-boride-based air battery600. The battery 600 may include two current collectors, an anodecurrent collector 602 and a cathode current collector 660. The anodecurrent collector 602 may serve as a point of contact for an anode 604.The anode current collector 602 may include carbon, nickel, copper,and/or any other metal or non-metal material suitable for use as adurable, electrically conductive support structure. Further, the anodecurrent collector 602 may be in contact with the anode 604. The anode604 is a source for Mg-ions. In this example, the anode 604 isconstructed from magnesium boride. However, the anode 604 may beconstructed from any magnesium boride containing material suitable forsupplying magnesium ions. The anode 604 may be doped with carbon and/orcarbon-derived materials such as graphite, graphene or any combinationor variation thereof. Suitable dopants may include at least one GroupIV/Group 14 elements, such as carbon, silicon, germanium, tin, lead,flerovium, Group V/Group 15 elements such as nitrogen, phosphorous,arsenic, antimony, bismuth, or any combination thereof. The anodecurrent collector 602 and the anode 604 may be a single layer, or thesame layer. Although not shown, one or more circuits may connect theanode 604 and the cathode 610 electrically.

Cathode 610 may include a metal foam/mesh as the current collector 660,constructed from various types of conductive materials, for example,carbon nanofiber, carbon nanotubes, and/or nanostructured catalysts. Thepore size, pore distribution, surface area, and electrochemical activityof the cathode layer 610 may be varied by selection of appropriate typesand mixing ratios of the materials desired. An exemplary cathode may beinclude several layers: a waterproof breathable layer 620, a gasdiffusion layer 630, and/or a catalyst layer 650 bound to a currentcollector 660 of a mesh/porous layer. As shown in FIG. 6, an exemplarycathode 610 may include several layers: a waterproof breathable layer620 and a gas diffusion layer 630, which may also include carbonconductive materials 640, and a catalyst layer 650. The waterproofbreathable layer 620 may be constructed of a water-repellant poroussubstance. The gas diffusion layer 630 may have a high porosity and ahigh electronic conductivity, and may be constructed from acetyleneblack containing hydrophobic materials such as PTFE. The catalyst layer650 may be primarily composed of active catalysts for the oxygenreduction reaction. In some case, noble metals such as Pt and Ag may beused in the catalyst layer 650 of the cathode 610. In other examples,N-doped carbonaceous, metal oxides, and/or metal oxide-carbonaceousmixtures may be used as catalysts in the catalyst layer 650 of thecathode 610. The battery 600 may also include a cathode currentcollector 660. The cathode current collector may serve as a point ofcontact for the cathode 610. The cathode current collector may beconstructed of carbon, nickel, aluminum, and/or any other metal ornon-metal material suitable for use as a lightweight, electricallyconductive support structure. Further, the cathode current collector 660and the cathode 610 may be a single layer of material.

The electrolyte 670 may be a non-aqueous electrolyte with a low vaporpressure. The electrolyte 670 may also have sufficient Mg-ionconductivity and oxygen solubility and preferably undergoes minimal orno side reactions with the anode and cathode materials. As describedherein, the electrolyte may include a non-aqueous solution containingGrignard reagents such as RMgX, where R is an alkyl or aryl. Forexample, R may be a methyl group, an ethyl group, and/or a propyl group.In addition, R may be a phenyl group, a methyl substituted phenyl(tolyl) group and/or a dimethyl substituted phenyl group.

FIG. 7 illustrates an exemplary method 700 to manufacture a rechargeablemagnesium-boride based air battery. The method 700 includes fabricating702 a first support structure, depositing 704 a magnesium boride basedanode onto the support structure, forming 706 a non-aqueous electrolyte,having Grignard reagents according to the formula RMgX, where thenon-aqueous electrolyte may be deposited onto the anode. The method 700continues with fabricating 708 a porous cathode layer for the cathode toabsorb oxygen, and depositing 710 the electrolyte layer onto the cathodelayer and/or a cathode current collector layer. The method 700 mayinclude an anode current collector. The anode current collector mayserve as a point of contact for the anode. The anode current collectormay be constructed using carbon, nickel, copper, and/or any other metalor non-metal material suitable for use as a durable, electricallyconductive support structure. Further, the anode current collector maybe in contact with the anode. The anode may be a source for metal-ions.The anode may be magnesium boride and/or any magnesium-based materialsuitable for supplying magnesium ions. The anode may be doped withcarbon, carbon-derived materials such as graphite, graphene and/or anycombination thereof. Suitable dopants may include Group IV/Group 14elements, such as carbon, silicon, germanium, tin, lead, flerovium,Group V/Group 15 elements such as nitrogen, phosphorous, arsenic,antimony, bismuth, or any combination thereof. The anode currentcollector and the anode may be constructed as a single layer ofmaterial.

The cathode in method 700 may include various types of conductivematerial such as carbon nanofiber, carbon nanotubes, and/ornanostructured catalysts. The pore size, pore distribution, surfacearea, and electrochemical activity of the cathode layer may be varied bythe selection of the appropriate types and/or mixing ratios of thematerials desired. The cathode may have several layers: a waterproofbreathable layer, a gas diffusion layer and/or a catalyst layer bound toa current collector made of a mesh/porous layer. The waterproof layermay be constructed from a water-repellant porous substance. The gasdiffusion layer may have a high porosity and/or electronic conductivity,and may be constructed, for example, from acetylene black and/orhydrophobic materials such as PTFE. The catalyst layer may primarilycontain active catalyst for the oxygen reduction reaction. Activecatalyst in the air cathode may be noble metals such as Pt and Ag. Otheractive catalyst materials for an air cathode may include N-dopedcarbonaceous, metal oxides and/or metal oxide-carbonaceous mixtures. Themethod 700 may include a cathode current collector. The cathode currentcollector may serve as a point of contact for the cathode. The cathodecurrent collector may include carbon, nickel, aluminum, and/or any othermetal and/or any non-metal material suitable for use as a lightweight,electrically conductive support structure.

The electrolyte in method 700 may be a non-aqueous electrolyte with alow vapor pressure. The electrolyte may also provide sufficient ionconductivity and oxygen solubility and preferably undergoes minimal orno side reactions with the magnesium oxide radical. The electrolyte mayinclude a non-aqueous solution containing Grignard reagents such asRMgX, wherein R may be an alkyl group or an aryl group. R may be amethyl group, an ethyl group, and/or a propyl group. R may be a phenylgroup, a methyl substituted phenyl (tolyl) group, and/or a dimethylsubstituted phenyl group.

It is noted that there are alternative ways of implementing theembodiments disclosed herein. While a number of exemplary aspects andembodiments have been discussed above, those of skill in the art willrecognize certain modifications, permutations, additions and subcombinations thereof. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive. Furthermore, the claimsare not to be limited to the details given herein, and are entitledtheir full scope and equivalents thereof.

The invention claimed is:
 1. An electrical device comprising: a currentcollector; and an active layer electrically connected to the currentcollector to form an anode, wherein: the active layer comprises aplurality of particles, a conductive additive, and a binder additive,the plurality of particles are present at a first amount between 50 wt %and 80 wt %, the conductive additive is at a second amount between 10 wt% and 30 wt %, and the binder additive is at a third amount of less thanor equal to 40 wt %, the plurality of particles have a first statecomprising at least two boron sheets with a plurality of magnesium atomsintercalated between the boron sheets resulting in a first compositionMgB₂, the plurality of particles have a second state comprising the atleast two boron sheets and a fraction, 1−y, of the plurality ofmagnesium atoms intercalated between the boron sheets resulting in asecond composition Mg_((1−y))B₂, where 0<y≤1, and the electrical deviceis capable of reversibly switching between the first state and thesecond state.
 2. The electrical device of claim 1 further comprising acathode comprising vanadium oxide.
 3. The electrical device of claim 1,wherein the conductive additive comprises acetylene black.
 4. Theelectrical device of claim 1, wherein the binder additive comprisespolyvinylidene fluoride.
 5. The electrical device of claim 1, whereinthe current collector comprises at least one of aluminum, copper, gold,or silver.
 6. The electrical device of claim 1, wherein the plurality ofparticles, the conductive additive, and the binder additive form aplurality of interstitial spaces in the active layer.
 7. The electricaldevice of claim 6, further comprising a liquid electrolyte, wherein atleast a portion of the liquid electrolyte is positioned within and fillsat least a portion of the plurality of interstitial spaces.
 8. Theelectrical device of claim 7, wherein the liquid electrolyte comprisesmagnesium tetrahydroborate.
 9. The electrical device of claim 8, whereinthe liquid electrolyte further comprises dimethoxyethane.
 10. Theelectrical device of claim 7, wherein the cathode and the anode areimmersed in the liquid electrolyte.
 11. A method for storing energy in abattery, the method comprising: immersing a first electrode and a secondelectrode in a liquid, non-aqueous, Mg²⁺ ion-containing, electrolytesolution; and applying a voltage across the first electrode and thesecond electrode, wherein: the first electrode comprises boron sheets ofboron atoms covalently bound together, with a plurality of magnesiumatoms reversibly intercalated between the boron sheets and ionicallybound to the boron atoms, the applying causes the reversibledeintercalation of a portion of the magnesium atoms from between theboron sheets, the applying creates a flux of Mg²⁺ ions from the firstelectrode into the electrolyte solution, the applying produces thereversible transfer of at least some of the Mg²⁺ ions from at least oneof the flux or from the electrolyte solution to the second electrode,such that the energy stored in the battery ranges from about 6 mAh/g toabout 10 mAh/g, and the second electrode comprises vanadium oxide andthe reversible transfer of at least some of the Mg²⁺ ions to the secondelectrode is by intercalation of Mg²⁺ ions into the vanadium oxide. 12.The method of claim 11 further comprising: applying a load across thefirst electrode and the second electrode, wherein the load: produces thereversible removal of magnesium atoms from the second electrode; createsa flux of Mg²⁺ ions from the second electrode into the electrolytesolution, and produces the reversible intercalation between the boronsheets of the first electrode of at least some of the Mg²⁺ ions from atleast one of the flux from the second electrode or the electrolytesolution.
 13. The method of claim 11, wherein the second electrodecomprises magnesium metal and the reversible transfer of at least someof the Mg²⁺ ions to the second electrode is by electrochemical platingof Mg²⁺ ions onto the magnesium metal.
 14. A rechargeablemagnesium-based air battery comprising: an anode layer formed ofmagnesium boride having the formula MgBx, wherein x≥1 and is depositedonto a first support structure; a porous cathode layer wherein the layerincludes positive active material that at least activates carbon forabsorbing oxygen in air, wherein oxygen gas is used as the positiveactive material and is deposited onto a second support structure; and anelectrolyte, wherein the electrolyte is a non-aqueous solution whereinthe solution contains Grignard reagents such as RMgX, wherein the anodelayer and cathode layer are connected electrically and the electrolyteis in contact with the first and second support structures.
 15. Thebattery of claim 14, wherein the first and second support structures arepositive and negative current collectors.
 16. The battery of claim 14,wherein the anode layer is doped.
 17. The battery of claim 14, whereinthe anode layer is doped with at least one of a Group IV/ Group 14element or a Group V/Group 15 element.
 18. The battery of claim 17,wherein the Group IV/Group 14 element comprises at least one of carbon,silicon, germanium, tin, lead, or flerovium.
 19. The battery of claim17, wherein the Group V/Group 15 element comprises at least one ofnitrogen, phosphorous, arsenic, antimony, or bismuth.